Bit1 as a tumor suppressor and a therapeutic target in NSCLC Abstract The work in this laboratory supported by this grant in the past three years has made significant contributions to the field of Bit1 functional biology particularly in the contxt of anoikis resistance and tumorigenicity of Non- Small Cell Lung Carcinoma (NSCLC), a deadly and the most prevalent form of lung cancer. Bit1 is a mitochondrial protein that is released to the cytoplasm following of loss of cell attachment, and associates with the transcriptional regulator protein Amino-terminal Enhancer of Split (AES) to trigger caspase-independent apoptosis. Our studies have shown that NSCLC cells are likely to bypass this pathway to become anoikis resistant and anchorage independent and provide the first evidence of the tumor suppressive function of Bit1 in NSCLC. Importantly, our recent findings indicate that Bit1 in addition to its anoikis function may negatively regulate Epithelial Mesenchymal Transition (EMT) in NSCLC cells. Hence, the observed tumor suppressive function of Bit1 may relate to its dual role in promoting anoikis and inhibiting EMT. This novel EMT regulatory function of Bit1 underscores its potential utility to circumvent the aggressive and metastatic phenotype of NSCLC. In line with Bit1 as a lung tumor suppressor, the TLE1 corepressor, a sole known inhibitor of Bit1 function, has recently been identified as a lung specific oncogene. Our work has contributed to the elucidation on the mechanism of the TLE1 oncogenic pathway, in part through blocking the Bit1 apoptotic pathway and promoting EMT in NSCLC cells. Our collective data supports a model wherein Bit1 functions to turn off the survival- and EMT-promoting gene regulatory functions of TLE1 in an AES dependent manner. In continuation of this project, we will investigate our hypothesis that Bit1 is a suppressor of lung epithelial cell transformation in vitro and lung tumorigenesis and cancer metastasis in vivo through its inhibitory effect on the oncogenic TLE1 transcriptional program. To test the hypothesis, we propose the following specific aims: 1) to study the role of the Bit1/AES/TLE1 pathway in the malignant transformation of human lung epithelial cells, 2) to determine the mechanism underlying the formation and activity of the Bit1/AES complex and the regulation of the TLE1 gene regulatory functions by the Bit1-AES complex, and 3) to determine the effects of enhanced and suppressed Bit1 and/or TLE1 expression on tumorigenicity and metastasis of NSCLC in vivo. These proposed studies will advance the fundamental knowledge on the mechanism by which the Bit1 pathway regulates lung tumorigenesis and progression and will contribute to potential translation of this pathway in the treatment of lung cancer. PHS398 (Rev. 5/01) Page Continuation Format Page